Actions of Volcanoes. 265 
reaching the surface, become consolidated, partly by their own 
weight, and partly by admixtures of lava. Thus pumice is so 
often found floating in the sea, having probably been washed 
off in these cases, in consequence of its buoyancy. Sabrina, 
abovementioned, was entirely carried away in this manner not 
long after its formation, having been composed entirely of 
light scoria. In all these cases of submarine eruption, flames 
and smoke have been seen to issue from the sea; marine.earth- 
quakes, (if such an expression may be used,) have been felt, and 
the water has been heated to boiling. 
But it is Humbolt’s opinion that, in many cases, these islands 
are principally formed by the elevation of the submarine strata ; 
and this notion is confirmed by a variety of facts, which may 
be witnessed in volcanic islands in many parts of the world, as 
in the West Indies, and in those of the African coast. This 
mode of formation is that which belongs to the cases here to be 
described, though they have hitherto escaped the attention of 
geologists, remarkable and interesting as they are. It will be 
seen that their interest is not merely limited to the proofs which 
they offer of volcanic elevation, or to the important conse- 
quences for a theory of the earth which thence follow, but that 
they illustrate and explain many collateral points which have 
been sources of great difficulty to geologists. The first of 
these cases is that of Italy, and the other is that of the Coral 
islands. 
In the former country there are found some remarkable allu- 
vial deposits, which, as far as observations yet go, have not 
been discovered elsewhere. Yet, if the theory which I have 
to offer respecting them be correct, it is probable that they are 
not thus limited; but that when their true nature and origin is 
more generally known, they will be found in other countries 
where similar circumstances are present. It is chiefly with the 
view of exciting the attention of such geologists as may have 
an Opportunity to pursue this interesting investigation, that I 
have given to this speculation the publicity of the Quarterly 
Journal. 
For the bare facts themselves we are indebted to Brocchi, 
